Johann W. Kolar

Bio: Johann W. Kolar is an academic researcher from ETH Zurich. The author has contributed to research in topics: Rectifier & Three-phase. The author has an hindex of 97, co-authored 965 publications receiving 36902 citations. Previous affiliations of Johann W. Kolar include Alstom & Infineon Technologies.

Optimal design of a 5kW/dm 3 / 98.3% efficient TCM resonant transition single-phase PFC rectifier

Abstract: In many applications single-phase PFC rectifiers should meet the demand for a high efficiency and a high power density at the same time. Depending on the weighting of these two design criteria, different topologies could be advantageous. As has been shown, with bridgeless PFC rectifiers an ultra high efficiency of 99.3% or a high power density of 5.6kW/dm3 could be realised. However, due to the hard switching operation it is not possible to achieve an exceptional efficiency and power density at the same time. Furthermore, SiC Schottky diodes are required for highly compact or highly efficient systems. Therefore, a triangular current mode (TCM), resonant-transition single phase PFC rectifier concept is presented in this paper, which overcomes both limitations. Besides a design procedure for optimising the chip area, also a simple and robust control concept, where a novel zero crossing detection concept is included, is explained and a prototype system as well as measurement results are presented for validating the concept and the design procedure.

Closed-Loop d ${\bm i}/$ d ${\bm t}$ and d ${\bm v}/$ d ${\bm t}$ IGBT Gate Driver

Abstract: This paper proposes a new concept for attaining a defined switching behavior of insulated-gate bipolar transistors (IGBTs) at inductive load (hard) switching, which is a key prerequisite for optimizing the switching behavior in terms of switching losses and electromagnetic interference (EMI). First, state-of-the-art gate driver concepts that enable a control of the IGBT's switching transients are reviewed. Thereafter, a highly dynamic closed-loop IGBT gate driver using simple passive ${\rm d}i_{\rm C}/{\rm d}t$ and ${\rm d}v_{\rm CE}/{\rm d}t$ feedbacks and employing a single analog PI-controller is proposed. Contrary to conventional passive gate drivers, this concept enables an individual control of the current and voltage slopes largely independent of the specific parameters or nonlinearities of the IGBT. Accordingly, a means for optimizing the tradeoff between switching losses, switching delay times, reverse recovery current of the freewheeling diode, turn-off overvoltage, and EMI is gained. The operating principle of the new gate driver is described and based on derived control oriented models of the IGBT, a stability analysis of the closed-loop control is carried out for different IGBT modules. Finally, the proposed concept is experimentally verified for different IGBT modules and compared to a conventional resistive gate driver.

Comparative evaluation of control methods for Inductive Power Transfer

Abstract: Inductive Power Transfer (IPT) has recently been proposed for application with Electric or Hybrid Electric Vehicles (EV/HEV), where a highly efficient system operation is demanded for the high-power transfer. Due to the high requirements on the regulation of the output power and the output voltage, and due to the large variations of the magnetic coupling, the control of these systems is a challenging task. In this paper, the frequency characteristics of a series-parallel compensated IPT system are discussed. Different control methods found in the literature are analyzed and a comparative evaluation of the current and voltage stress in the transmission coils, the resonant capacitors, and the semiconductors in the primary-side inverter is presented. It is shown that the dual control method offers a number of advantages in the controllability and potentially lower losses compared to the frequency control which is commonly used.

High-Performance Planar Isolated Current Sensor for Power Electronics Applications

Abstract: A planar current sensor, comprised of a magnetic current transformer and a hall-effect element, is presented. The sensor has a broad frequency bandwidth from dc up to 30 MHz, a high current rating (40-A dc), superior linearity, high EMI immunity, small size, robustness, and low realization cost. The main design formulations are given analytically; simulations and finite-element results are presented for verification. Experimental results of current step response and dv/dt immunity are included.

Artificial Neural Network (ANN) Based Fast and Accurate Inductor Modeling and Design

Abstract: This paper analyzes the potential of Artificial Neural Networks (ANNs) for the modeling and optimization of magnetic components and, specifically, inductors. After reviewing the basic properties of ANNs, several potential modeling and design workflows are presented. A hybrid method, which combines the accuracy of 3D Finite Element Method (FEM) and the low computational cost of ANNs, is selected and implemented. All relevant effects are considered (3D magnetic and thermal field patterns, detailed core loss data, winding proximity losses, coupled loss-thermal model, etc.) and the implemented model is extremely versatile (30 input and 40 output variables). The proposed ANN-based model can compute 50'000 designs per second with less than 3% deviation with respect to 3D FEM simulations. Finally, the inductor of a 2 kW DC-DC buck converter is optimized with the ANN-based workflow. From the Pareto fronts, a design is selected, measured, and successfully compared with the results obtained with the ANNs. The implementation (source code and data) of the proposed workflow is available under an open-source license.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Multilevel inverters: a survey of topologies, controls, and applications

Abstract: Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.

Recent Advances and Industrial Applications of Multilevel Converters

Abstract: Multilevel converters have been under research and development for more than three decades and have found successful industrial application. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide readers with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multilevel converters and how multilevel converters are becoming an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.